In previous work (annual reports, 1984-1987), we cloned and sequenced nine of the ten genes of human respiratory syncytial virus strain A2, which represents RSV antigenic subgroup A. Also, cloning and sequencing was extended to the Long strain, which is a second strain from antigenic subgroup A, and the 18537 strain, which represents subgroup B (annual reports, 1986 and 1987). To continue the structural analysis of RSV genomic RNA (vRNA) and its encoded mRNAs and proteins, cDNA cloning and sequencing is underway for the L gene of strain A2 by direct RNA sequencing and by cDNA cloning and sequencing. This will complete the sequencing of vRNA of the prototype A2 strain. The availability of cDNAs and sequences representing the entire vRNA will be an important step towards the goal of expressing infectious RSV from cloned cDNA.